1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) display and related method, and more particularly, to an LCD display capable of improving color contrast phenomenon while displaying an image and a related method for improving such phenomenon.
2. Description of the Prior Art
Liquid Crystal Display (LCD) panels having a plurality of transistors and capacitors in an array can display vivid images and are widely used all over the world. The LCD panels, due to their light weight, low power consumption, and no radiation, have increasingly replaced traditional Cathode Ray Tube (CRT) monitors and are also used in portable electrical devices such as notebook computers and Personal Digital Assistants (PDAs).
An LCD display includes a liquid crystal layer comprising liquid crystal molecules sandwiched between two indium tin oxide sheets of glass (ITO glass). One of the glass layers serves as a pixel electrode and the other serves as a common electrode. The alignment of the sandwiched liquid crystal molecules changes as the voltage across the two electrodes changes. Therefore, various gray levels are provided based on different alignments of the liquid crystal molecules.
In general, as a person skilled in this art is aware, the voltage across the two electrodes has two polarities. A voltage of the pixel electrode larger than a voltage of the common electrode is called positive polarity, and a voltage of the common electrode larger than that of the pixel electrode is called negative polarity. If absolute values of the voltage difference across the two electrodes are identical, no matter whether the voltage value of the pixel electrode or that of the common electrode is higher, an identical gray level is obtained. However, an opposed voltage difference value across the two electrodes results in the opposed alignment of the liquid crystal molecules.
From a view of long-term sum effect, if the voltage across the two electrodes tends toward either polarity for a long time, the alignment of the liquid crystal molecules will fail to be varied based on the required control voltage, resulting in the display of incorrect gray levels. In an extreme situation, it is possible that if the voltage across the two electrodes tends toward either polarity for a long enough time, even if no voltage is applied, the liquid crystal molecules will still fail to be aligned because of varying electrical fields due to malfunctioning of the liquid crystal molecules. As a result, in order to prevent the liquid crystal molecules invalidity as the voltage applied across the two electrodes tends toward either polarity, the voltages across the two electrodes are periodically switched between positive polarity and negative polarity.
Please refer to FIG. 1, which illustrates a diagram of voltage applied on the liquid crystal molecules for a pixel unit in response to the display data combined with the polarity in sequence. In general, a voltage Vcom applied on the common electrode voltage is at a constant 8V, and the display data is combined with alternate positive and negative polarities. As shown in FIG. 1, an absolute value of a voltage difference between the gray-level voltage (12V) corresponding to the gray-level of the display data (+FF) and the common voltage Vcom is 4V. Similarly, an absolute value of a voltage difference between the gray-level voltage (4V) corresponding to the gray-level of the display data (−FF) and the common voltage value Vcom is 4V. Therefore, identical absolute values of voltage differences but exactly opposed polarities cause opposed alignments of the liquid crystal molecules and indicate the same gray-level.
Please refer to FIG. 5, which illustrates a relationship of a reflectance versus voltage difference corresponding to RGB curves. As can be seen in FIG. 5, smooth RGB curves in an interval of 0-1V are illustrated. In other words, in the interval of 0-1V, each of the RGB curves correspond to high reflectance values but low reflectance variety. This indicates that, in the interval of 0-1V, higher luminance as well as low color contrast is obtained. Because people's eyes are more sensitive to bright color than to dark color, it is hard for people's eyes to distinguish color contrast corresponding to the grey-scale data defined in the range of 0-1V. Consequently, a conventional LCD requires improvement.